A thallium(I) tetranuclear cubic cage unit in an interpenetrated supramolecular polymer: A new precursor for the preparation of Tl 2O3 nanostructures

Article abstract of DOI:10.1016/j.poly.2011.06.027

A new thallium(I) supramolecular polymer, [Tl₄(μ₃- 4-BN)₄]_n (1) [9-HBN = 4-hydroxy benzonitrile], with a disordered cubic cage structural unit has been synthesized and characterized. The single-crystal X-ray dat

Full text of DOI:10.1016/j.poly.2011.06.027

Polyhedron 30 (2011) 2459–2465
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Polyhedron
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A thallium(I) tetranuclear cubic cage unit in an interpenetrated
supramolecular polymer: A new precursor for the preparation of Tl2O3
nanostructures
⇑
Kamran Akhbari, Ali Morsali
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A new thallium(I) supramolecular polymer, [Tl4(l3-4-BN)4]n (1) [9-HBN = 4-hydroxy benzonitrile], with a
Received 4 May 2011
Accepted 15 June 2011
Available online 23 July 2011
disordered cubic cage structural unit has been synthesized and characterized. The single-crystal X-ray
data of compound 1 shows one type of TlI ion in the tetranuclear cubic cage structure with a coordination
number of three. In addition to two intra cage thallophilic interactions in 1, each thallium(I) atom has a
weak TlÁ Á ÁN secondary interaction with the nitrile group of the 4-BNÀ ligand. Finally the Tl-ions attain the
O3TlÁ Á ÁNTl2 coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metal. The self
assembly between the benzonitrile groups of one cubic cage structure with an adjacent one with a TlÁ Á ÁN
Keywords:
Cubic cage unit
Thallium(I)
Supramolecular
Thallium(III) oxide
Nanostructures
CTAB
short contact, by p–p stacking and weak hydrogen bonding interactions, results in the formation of a new
interpenetrating thallium(I) supramolecular polymer. The thermal stability of 1 was studied by thermo
gravimetric (TG) and differential thermal analyses (DTA). Nanostructures of thallium(III) oxide were pre-
pared from a calcination process of compound 1 fine powder at 743 K. These nanostructures were char-
acterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
with those of other metals, but the chemistry and coordination
behavior of thallium(I) ion is very unique and attractive [14], and
During the last two decades supramolecular compounds and
especially coordination polymers have received great attention
and the number of their synthesized compounds is still growing,
which is mainly due to their potential application in various fields
such as microelectronics, non-linear optics, ion exchange, catalysis,
gas storage, separation and luminescence [1–6]. In modern coordi-
nation chemistry the role of most metals as clustering centers for
ligands appears to be predictable and the coordination number
and the coordination geometry can be extrapolated for most of
the common metal/ligand combinations with quite high certainty.
Although this is generally true, the situation is surprisingly difficult
for main group metals in their low oxidation states, in which they
are assigned lone pairs of electrons [7–12]. Although such a pair of
s electrons beyond a completed shell is always stereoactive in the
thallium(I) complexes with a hemi-directed environment, lower
coordination number (three to five) and an obvious gap in TlI coor-
dination sphere, this activity cannot be predicted in complexes
with higher coordination number (6–12) and a holo-directed envi-
ronment [13]. Formation of polymers with main group metal ions
such as thallium(I) is disproportionately sparse when compared
the number of TlI supramolecular compounds is very much lower
than for other metal ions. TlI favors the formation of neutral species
with anionic ligands. One-dimensional polymers constitute a great
portion of the thallium(I) supramolecular compounds, whilst two-
and three-dimensional polymers are less common. This may be re-
lated to the existence of a vacant site on the thallium(I) environ-
ment and the hemi-directed coordination sphere of the TlI ion
due to the stereo-chemical activity of its lone pair, which was fre-
quently observed, and effects related to the structure, size and
rigidity of the ligands. In addition, thallium(I) usually favors the
formation of TlÁ Á ÁTl, TlÁ Á ÁC and TlÁ Á ÁH secondary interactions, espe-
cially on its vacant coordination sphere with the stereo-chemically
active lone pair, which indicates that thallium(I) ions have the
capacity to act as both a Lewis acid and a Lewis base [14]. Contin-
uing our previous works on TlI supramolecular compounds [15–22]
and to extend the number of thallium(I) supramolecular com-
pounds with other organic ligands, in this work we wish to report
another supramolecular compound containing the TlI ion, having a
tetranuclear cubic cage unit, formed with the 4-hydroxy benzoni-
trile ligand (4-HBN). With phenolate derivative ligands, TlI usually
forms two structures: disordered cubic units, which are retained in
the solution state with thallophilic interactions, and stair-like poly-
mers. In this case we observed the tetranuclear cubic cage struc-
ture again. In addition to the synthesis and characterization of
⇑
Corresponding author. Tel./fax: +98 21 82884416.
E-mail address: Morsali_a@modares.ac.ir (A. Morsali).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.06.027

2460
K. Akhbari, A. Morsali / Polyhedron 30 (2011) 2459–2465
Scheme 1. The produced materials from the reaction of the 4-HBNÀ ligand with thallium(I) nitrate by two different methods and fabrication of thallium(III) oxide
nanostructures from the resulting materials.
Table 1
Table 2
Crystal data and structure refinement for compound [Tl4(l3-4-BN)4] (1).
Selected bond lengths (Å) and angles (°) for compound [Tl4(l3-4-BN)4]n (1).
Empirical formula
Formula weight
T (K)
C7H4NOTl
322.48
273(2)
Tl1–O1
Tl1–O1i
Tl1–O1ii
2.487(11)
2.674(12)
2.704(12)
O1–Tl1–O1i
79.2(4)
78.6(4)
65.1(4)
O1–Tl1–O1ii
O1i–Tl1–O1ii
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
tetragonal
I 41/a
Symmetry transformations used to generate equivalent atoms; i: Ày + 3/4, x + 1/4,
z + 1/4; ii: Àx + 1/2, Ày, z + 1/2.
16.8343(18)
16.8343(18)
10.086(2)
90.00
90.00
90.00
2858.3(7)
16
2.998
b (Å)
c (Å)
using a Heraeus CHN-O-Rapid analyzer. Melting points were mea-
sured on an Electrothermal 9100 apparatus and are uncorrected.
IR spectra were recorded using Perkin-Elmer 597 and Nicolet
510P spectrophotometers. The thermal behavior was measured
with a PL-STA 1500 apparatus between 40 and 610 °C in a static
atmosphere of nitrogen. Crystallographic measurements were
made using a Bruker APEX area-detector diffractometer. The
intensity data were collected using graphite monochromated
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmÀ3
)
Absorption coefficient (mmÀ1
F(0 0 0)
)
22.522
2272
Crystal size (mm3)
0.13 Â 0.12 Â 0.11
2.35–25.10
À20 6 h 6 12
À18 6 k 6 20
À12 6 l 6 11
1277
1032 [Rint = 0.2371]
semi-empirical from
equivalents
0.1908 and 0.1578
full-matrix least-squares on F2
1277/1/92
Mo K
and refined by full-matrix least-squares techniques on F2. Struc-
ture solution and refinement was accomplished using the SHELXL
a radiation. The structure was solved by direct methods
h Range for data collection (°)
Index ranges
-
97 program packages [24]. The molecular structure plot and
simulated XRD powder pattern based on single crystal data were
prepared using Mercury software [25]. X-ray powder diffraction
(XRD) measurements were performed using a Philips X’pert dif-
Reflections collected
Independent reflections
Absorption correction
fractometer with monochromatized Cu K
a radiation. The samples
Maximum and minimum transmission
Refinement method
were characterized with a scanning electron microscope with a
gold coating.
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.142
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0741
wR2 = 0.1958
R1 = 0.0824
wR2 = 0.2001
0.502 and À2.559
2.2. Synthesis of [Tl4(l3-4-HBN)4] (1), preparation of its single crystals
and Tl2O3 nanostructures
Largest difference in peak and hole (e ÅÀ3
)
The 4-hydroxy benzonitrile ligand (2 mmol (0.238 g)) was dis-
solved in 20 ml methanol and this was mixed and stirred with a
solution of 2 mmol (0.114 g) KOH in 3 ml H2O. A solution of
2 mmol (0.533 g) TlNO3 in 5 ml H2O was then added to the mix-
ture, and the resulting solution was refluxed for 4 h. After filtering,
it was allowed to evaporate for several days, whereupon suitable
yellow crystals were obtained. The crystals were washed with ace-
tone and air dried, d.p. = 216 °C, yield: 0.373 g (58%). IR (selected
bands; in cmÀ1): 421 m, 452 m, 544 m, 645 w, 703 s, 810 m, 836
s, 992 w, 1102 m, 1160 s, 1203 m, 1284 s, 1351 w, 1401 s, 1580
s, 2165 s. Anal. Calc. for C7H4NOTl: C, 26.05; H, 1.24; N, 4.34. Found:
C, 25.82; H, 1.30; N, 4.27%. In order to obtain Tl2O3 nanostructures,
a fine powder of compound 1, after well grinding single crystals of
1, was calcinated at 743 K in a furnace and under a static atmo-
sphere of air for 5 h.
this complex, a mixture of TlBr nanoballs and nanorods were pre-
pared by water-in-oil microemulsion-based methodology [23]. A
fine powder of compound 1 and TlBr nanostructures were used
for the preparation of Tl2O3 nanostructures.
2. Experimental
2.1. Materials and physical techniques
All reagents for the synthesis and analysis were commercially
available and used as received. Microanalyses were carried out

K. Akhbari, A. Morsali / Polyhedron 30 (2011) 2459–2465
2461
Fig. 1. View of the Tl environment; showing the disordered tetranuclear cubic cage secondary building unit in [Tl4(l3-4-BN)4]n (1).
of 30-1351. Another 10.7 ml of the mixture was transferred to a
30-ml Teflon-lined stainless-steel autoclave and kept at 373 K for
1 h. After being cooled to room temperature, nanostructures of
thallium(I) bromide (yellow-white crystalline products) were sep-
arated by centrifugation, and washed with deionized water and
absolute ethanol several times, and then dried at 353 K for 6 h.
M
O
O
M
Tl
O
M
M
O
O
CN
Tl
Tl
3. Results and discussion
Scheme 2. The coordination mode of the ligand 4-BNÀ in compound 1 (left) and the
schematic representation of the tetranuclear cubic cage unit (right).
3.1. Structure description
Scheme 1 shows the reaction between thallium(I) nitrate and 4-
HBNK by two different methods.
2.3. Preparation mixture of TlBr nanoballs and nanorods, by the
microemulsion-based methodology with a cationic surfactant, and
Tl2O3 nanostructures
The reaction between 4-hydroxy benzonitrile (4-HBN), KOH and
subsequently TlI(NO3) provided crystalline materials of the general
formula [Tl4(l3-4-BN)4]n (1). Determination of the structure of this
Mixture of thallium(I) bromide nanoballs and nanorods were
prepared by the microemulsion-based methodology with cetyltri-
methylammonium bromide (CTAB) as a cationic surfactant [26].
In a typical procedure, two 10.70 ml microemulsion solutions were
prepared by adding 1.54 ml 0.5 M TlNO3 and 1.54 ml 0.5 M 4-
HBNK aqueous solutions to a n-heptane/CTAB/n-propanol system
(n-propanol/CTAB = 4.10 (molar ratio), H2O/CTAB = 20 (molar ra-
tio), [CTAB] = 0.4 M), respectively, which were stirred for 30 min
at 308 K. The 4-HBNK microemulsion became transparent, but
the TlNO3 microemulsion formed a white precipitate. After that,
the two solutions were mixed slowly and stirred for another
60 min at 308 K. Two types of precipitates were distinguishable,
a large amount of white solid, which was CTAB (confirmed by an
IR spectrum comparison of CTAB and this white solid) and a small
amount of a yellow-white crystalline solid which consisted of TlBr
nanoballs and nanorods (confirmed by XRD pattern comparison of
this compound with the standard patterns of thallium(I) bromide
with a JCPDS card number of 08-0486). The 10.7 ml of this mixture
was separated by centrifugation and the obtained product was red-
ispersed in a mixture of ethanol and water. This isolation process
was repeated five times to give purified TlBr nanostructures in a
powdery form. In order to obtain Tl2O3 nanostructures from this
precursor, half of this precipitate was calcinated at 873 K in a fur-
nace and under a static atmosphere of air for 5 h. The black fine
powder obtained was identified as Tl2O3 nanostructures, con-
firmed by an XRD pattern comparison of this compound with the
standard patterns of thallium(III) oxide with a JCPDS card number
compound by X-ray crystallography (Tables 1 and 2) showed the
compound to have a novel tetranuclear cubic cage unit (Fig. 1 and
Scheme 2) containing four Tl+-ions with coordination numbers of
three. The Tl atoms are coordinated by three phenolic oxygen atoms
with Tl–O distances of ca. 2.48–2.70 Å. The phenolic oxygen atom of
the ‘4-BNÀ’ ligand acts as bridging group (totally with three bonding
interactions, Fig. 1 and Scheme 2). There are interactions between
Tl1 and the two other thallium atoms in the cage. The distances be-
tween them are 3.833 Å, smaller than the sum of van der Waals radii
of two TlI ions [27]. The distances between the other thallium atoms
within the cage are 4.510 Å, longer than the sum of van der Waals ra-
dii of two TlI [14]. Hence, two metallophilic TlÁÁÁTl interactions for the
Tl1 atoms in compound [Tl4(l
3-4-BN)4]n may be considered. Each TlI
ion also has a short contact with the nitrogen atom of the 4-BNÀ li-
gand (3.166 Å). Thus, the Tl-ions in this compound have an
O3TlÁ Á ÁNTl2 coordination sphere. In [Tl4(l3-4-BN)4]n, the lone pair
of the Tl(I) atoms is ‘active’ in the solid state. Indeed, the arrange-
ment of O atoms suggests a gap or hole in the coordination geometry
around the Tl(I) center (Fig. 1), a gap possibly occupied by a ‘stereo-
active’ electron lone pair. Hence, the geometry of the nearest coordi-
nation environment of every Tl(I) atom is likely to be caused by the
geometrical constraints of coordinated O and Tl atoms and by the
influenceof a stereo-chemically ‘active’electronlone pair ontheme-
tal. Four thallium atoms and four oxygen atoms of 4-BNÀ anions
form an interesting cage with a distorted cubic geometry (Fig. 1
and Scheme 2). As can be observed in Figs. 2 and S1, a
p–p stacking
interaction between the parallel aromatic rings of adjacent units

2462
K. Akhbari, A. Morsali / Polyhedron 30 (2011) 2459–2465
Fig. 2. A fragment of three dimensional supramolecular polymer in [Tl4(
interactions between the parallel aromatic rings of adjacent units (Tl = purple, O = red, C = gray, N = blue and H = white). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
l3-4-BN)4]n (1), showing the TlÁ Á ÁN short contact with green dashed lines and p–p stacking
Fig. 3. A fragment of three dimensional supramolecular polymer in [Tl4(
C = gray, N = blue and H = white). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
l3-4-BN)4]n (1), showing lozenge channals of 1.4 Â 2.1 nm along the b axis (Tl = purple, O = red,

K. Akhbari, A. Morsali / Polyhedron 30 (2011) 2459–2465
2463
120
100
80
60
40
20
0
80
TG
DTA
60
40
20
0
-20
0
100
200
300
400
500
600
700
Temperature(°C)
Fig. 4. Thermal behavior of the compound [Tl4(l3-4-BN)4]n (1).
has a distance of 3.838 Å, which can be considered as a normal p–p
stacking interaction [28,29]. A weak C–HÁ Á ÁN hydrogen bonding
interaction with a bond length of 2.749 Å and a bond angle of
162.70° stabilizes this supramolecular structure (Fig. S2). Self
assembly between the benzonitrile groups of one cubic cage struc-
ture with an adjacent one with a TlÁ Á ÁN short contact, by
p–p stack-
ing and weak hydrogen bonding interactions, results in the
formation of a new thallium(I) supramolecular polymer (Fig. 3). As
could be observed in Fig. 3, [Tl4(l3-4-BN)4]n forms a 3D supramolec-
ular compound with 1.4 Â 2.1 nm lozenge vacant channals along the
b axis. These lozenge guest free channals couldbe observedalong the
a axis too (Fig. S3). Initially, this may indicate that this compound is
porous, but further structural considerations indicate that these
pores are occupied by another interpenetrating network, resulting
in a completely packed supramolecular polymer with no vacant
sites. A search in the Cambridge Structural Database (CSD) shows
that there are only seven TlI compounds with this tetranuclear cubic
cage unit; [TlOCH2CF3]4 [30], [Tl(
NO2)]4 [32], [Tl(OC6H3(3,5-CF3)2)]4 [33], [Tl(OCH2-tBu)]4 [34],
[Tl( 3-OC6H3(2,4-Cl2))]4 [21] and [Tl4{ 6-OC6H4(SO2)C6H4O}2]n
l3-OSiPh3)]4 [31], [Tl(p-OC6H4-
l
l
[35]. Another search in the Cambridge Structural Database (CSD)
shows that 1434 compounds have this tetranuclear cubic cage unit,
and this unit (Scheme 2) could be observed for various different me-
tal ions such as; Li+ [36], Na+ [36], K+ [37], Mg2+ [38], Ba2+ [39], Ti2+
[40], Cr3+ [41], Mn2+ [42], Fe2+ [42], Co2+ [42], Ni2+ [42], Cu2+ [43],
Zn2+ [42], Re+ [44], Ru2+ [45], Cd2+ [46], Ag+ [47], Pb2+ [48], Yb2+
[49] and Gd3+ [50].
Thermo gravimetric (TG) and differential thermal analyses (DTA)
of compound 1 single crystals shows that this compound is stable up
to 185 °C in a static atmosphere of nitrogen (Fig. 4), at which tem-
perature pyrolysis of compound 1 starts, and this continues up to
470 °C. Thus removal of 4-HBNÀ occurs between 185 and 470 °C
and this pyrolysis process is accompanied by two exothermic effects
at 230 and 420 °C. Fig. 5a shows the simulated XRD pattern from the
single crystal X-ray data of compound 1 and Fig. 5b shows the XRD
Fig. 5. XRD patterns; (a) simulated pattern based on single crystal data of
compound 1, (b) fine powder of compound 1 after the well grinding process, (c)
nanostructures of Tl2O3 prepared by the calcination process of compound 1 fine
powder at 743 K, (d) TlBr nanostructures prepared by the reverse micelles
technique and (e) thallium(III) oxide prepared by thermal treatment of TlBr at
873 K.
z = 16, which are close to the reported values, (JCPDS card number
30-1351). SEM images (Fig. 6) of the residue obtained from calcina-
tion of compound 1 fine powder at 743 K show that thallium(III)
oxide with a nanostructural surface was formed. Microemulsion-
based methodology, which uses reverse micelles of cationic
surfactants such as cetyltrimethylammonium halides [CTAX, X = B
(bromide), C (chloride)], is frequently used for the preparation of
nanometer-sized metal coordination nano-polymers (MCNPs) [51]
and nanometer-sized metal-organic-frameworks (NMOFs) [23].
We used this methodology for the preparation compound 1 nano-
structures from the initial reagents by the reaction of the Tl+ ion
and 4-HBNÀ ligand, but the XRD pattern of the residue (Fig. 5d)
matches the standard patterns of thallium(I) bromide, with the lat-
tice parameters a = 3.9850 Å and z = 1, which are close to the
pattern of [Tl4(l3-4-BN)4]n fine powder, prepared from well grind-
ing compound 1 single crystals. Acceptable matches, with slight dif-
ferent in 2h, were observed between the simulated from single-
crystal X-ray data pattern (Fig. 5a) and the experimental powder
X-ray diffraction pattern for a fine powder of compound 1 prepared
by a grinding process (Fig. 5b). The results of the XRD powder pat-
terns indicate that no structural changes occurred during the grind-
ing process. In order to prepare Tl2O3 nanostructures from the
compound 1 precursor, a fine powder of compound 1, obtained from
grinding compound 1 single crystals, was calcinated at 470 °C.
Fig. 5c shows the XRD pattern of the residue obtained from the cal-
cination process. The obtained patterns match the standard pat-
terns of cubic Tl2O3 with the lattice parameters a = 10.546 Å and

2464
K. Akhbari, A. Morsali / Polyhedron 30 (2011) 2459–2465
reported values, (JCPDS card number 08-0486). A SEM image of the
resulting product shows the formation of a mixture of TlBr nano-
balls and nanorods (Fig. 7). Heat treatment of these TlBr nanostruc-
tures in a teflon-lined stainless-steel autoclave at 373 K for 1 h
shows that an agglomeration process occurred, and the morphology
and size distribution of these nanostructures changed (Fig. S4).
Thus, this technique was not successful for the preparation com-
pound 1 nanostructures. Calcination of TlBr powder at 873 K, re-
sulted in the formation of black residue, the XRD pattern of which
(Fig. 5e), matches with the standard patterns of thallium(III) oxide,
with the lattice parameters mentioned above. The morphology,
structure and size of the sample which was prepared by the calcina-
tion process on the TlBr nanostructures were investigated by scan-
ning electron microscopy (SEM). The SEM images show the
formation of cubic Tl2O3 structures with a nanostructural surface
(Fig. 8).
Fig. 6. SEM image of Tl2O3 nanostructures, prepared by the calcination process of
compound 1 fine powder at 743 K.
4. Conclusions
Thallium(III) oxide nanostructures were prepared from a calci-
nation process of [Tl4(
sion-based methodology was not successful for the syntheses of
compound nano-structures, and TlBr nanostructures were
l3-4-BN)4]n (1) at 743 K. The microemul-
1
formed. Thermal treatment of the TlBr nanostructures resulted in
the formation cubic structures of Tl2O3 with a nanostructural sur-
face. The Tl-ions in this compound have a O3TlÁ Á ÁNTl2 coordination
sphere with a stereo-chemically ‘active’ electron lone pair on the
metal. Four thallium atoms and four oxygen atoms of 4-BNÀ anions
form an interesting cage with a distorted cubic geometry. Self
assembly between the benzonitrile groups of one cubic cage struc-
ture with an adjacent one with a TlÁ Á ÁN short contact, by
p–p
stacking and weak hydrogen bonding interactions, results in the
formation of a new interpenetrating thallium(I) supramolecular
polymer.
Fig. 7. SEM image of TlBr nanostructures, prepared by the reverse micelles
technique using a cationic CTAB surfactant.
Acknowledgement
Support of this investigation by Tarbiat Modares University is
gratefully acknowledged.
Appendix A. Supplementary data
CCDC 639612 contains the supplementary crystallographic data
for compound 1. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2011.06.027.
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